A 3G network architecture defined by the 3rd Generation Partnership Project (The 3rd Generation Partnership Project, 3GPP for short) in the Wideband Code Division Multiple Access (Wideband Code Division Multiple Access, WCDMA for short) R4 standard mainly includes: a radio access network (Radio Access Network, RAN for short), a core network (Core Network), and a bearer network (Backbone). A generalized RAN includes an air interface (Air Interface) between a terminal and a base station, that is, a Uu interface, and an Iub interface between the base station and a base station controller. For transmission and bearing, the RAN generally refers to an aggregation network between a base station and a base station controller.
With the development of a mobile network from 2G, to 3G, and then to a Long Term Evolution (Long Term Evolution, LTE for short) technology, a mobile communications network is evolving in a direction of broadband, packet, and flatting, and a mobile all (ALL IP) Internet Protocol (Internet Protocol, IP for short) network becomes an irreversible trend. The RAN is also faced with a trend of transforming from a conventional time division multiplexing (Time Division Multiplex, TDM for short)/asynchronous transfer mode (Asynchronous Transfer Mode, ATM for short) RAN to an IP RAN. The IP RAN based on an IP/Multiprotocol Label Switching (Multi-Protocol Label Switching, MPLS for short) packet data technology has a higher bandwidth, supports statistical multiplexing of a data service, can better support a future broadband mobile service, adopts a same technology as an IP backbone network, and has better consistency and integration with the backbone network; therefore, the IP RAN is widely used. The IP RAN mainly includes: an access ring at a base station side formed by ATN devices or other types of devices, and an aggregation ring formed by CX devices or other types of devices. Generally, each device on the aggregation ring may access 10 to 20 access rings. Each access ring is formed by about 10 ATN devices and the like. Two high-end CX devices or other types of devices are generally disposed in the aggregation ring as gateways which are connected to a core network. An ATN device or another type of device on the access ring is called a cell site gateway (Cell Site Gateway, CSG for short) or a multi-service transport gateway (Multi-Service Transport Gateway, MSTG for short). A CX device or another type of device on the aggregation ring is called a radio network controller site gateway (RNC Site Gateway, RSG for short) or a multi-service aggregation gateway (Multi-Service Aggregation Gateway, MSAG for short). A device that is on the access ring and the aggregation ring at the same time is a core router (Provider Router) in an MPLS virtual private network (Virtual Private Network, VPN for short), that is, a P device; other devices on the access ring or the aggregation ring are provider edges (Provider Edge, PE for short) in the MPLS VPN.
In IP RAN solutions, according to different service types, an end-to-end pseudo wire (Pseudo Wire, PW for short) or a Layer 3 VPN (L3VPN for short) may be deployed between a PE (that is, CSG) on the access ring and a PE (that is, RSG) on the aggregation ring to carry a service. An L3VPN and a PW generally use an MPLS traffic engineering (Traffic Engineering, TE for short) tunnel to traverse a network.
In an IP RAN network, when a service uses an MPLS TE tunnel, in order to ensure high reliability of the network, Bidirectional Forwarding Detection (Bidirectional Forwarding Detection, BFD for short) needs to be used to detect an MPLS TE label switched path (Label Switch Path, LSP for short). When BFD detects that a network link or node encounters a fault, switching a service path may be triggered at an ingress node, so as to achieve an objective of protecting the service. However, because an MPLS TE LSP is unidirectional, a BFD forward detection message is sent through the MPLS TE LSP, but a reverse detection message is sent through another path, such as an IP path. In this way, when a reverse path is blocked, a BFD status is set to down (down), but actually a path status of a forward MPLS TE LSP is normal, so that an objective of ensuring high reliability of a service cannot be achieved.